The present invention pertains to a rotary tool for penetrating the earth strata such as, for example, a roof drill bit or a tri-cone drill bit, that has one or more hard inserts at the axially forward end. In the case of a roof drill bit, such a rotary tool has been typically used to drill holes in a mine roof. In the case of a tri-cone drill bit, such a rotary tool has been used to drill holes for oil wells and the like.
The typical rotary tool has a hard insert affixed at an axially forward end. The hard insert is the part of the rotary tool that first impinges upon the earth strata or other substrate. The hard insert is comprised of a tungsten carbide cermet (WC-cermet), also known as cobalt cemented tungsten carbide and WC-Co. Here, a cobalt binder (Co-binder) cements tungsten carbide particles together. Although hard inserts made of a WC-cermet having a Co-binder have achieved successful results, there are some drawbacks.
One drawback is that up to about 45 percent of the world's primary cobalt production is located in politically unstable regions (e.g., political regions that have experienced either armed or peaceful revolutions in the past decade and could still experience additional revolutions). About 15 percent of the world's annual primary cobalt market is used in the manufacture of hard materials including WC-cermets. About 26 percent of the world's annual primary cobalt market is used in the manufacture of superalloys developed for advanced aircraft turbine engines--a factor contributing to cobalt being designated a strategic material. These factors not only contribute to the high cost of cobalt but also explain cobalt's erratic cost fluctuations. Consequently, cobalt has been relatively expensive, which, in turn, has raised the cost of the WC-cermet hard insert, as well as the cost of the overall rotary tool. Such an increase in the cost of the rotary tool has been an undesirable consequence of the use of Co-binder for the hard insert. Therefore, it would be desirable to reduce cobalt from the binder of WC-cermet hard inserts.
Furthermore, because of the principal locations of the largest cobalt reserves, there remains the potential that the supply of cobalt could be interrupted due to any one of a number of causes. The unavailability of cobalt would, of course, be an undesirable occurrence.
Rotary tools operate in environments that are corrosive. While the WC-cermet hard inserts have been adequate in such environments, there remains the objective to develop a hard insert which has improved corrosion resistance while maintaining essentially the same wear characteristics of WC-cermet hard inserts.
While the use of WC-cermet hard inserts has been successful, there remains a need to provide a hard insert which does not have the drawbacks, i.e., cost and the potential for unavailability, inherent with the use of cobalt set forth above. There also remains a need to develop a hard insert for use in corrosive environments that possess improved corrosion resistance without losing any of the wear characteristics of WC-cermets having a Co-binder.